Steam generating system

ABSTRACT

A steam generating system comprising an enlarged water tank receiving an elongated fire tube therethrough. The fire tube has a burner and steam coil mounted on a movable frame therein and selectively retractable therefrom into an enclosed control room provided at one end of the water tank and including controls, pump means, cleaning means, and the like. The fire tube acts so as to preheat the water subsequently pumped from the tank and through the steam generating coil for ultimate discharge from the system.

United States Patent [72] Inventor Ernest R. Mnckelrath 2,625,915 l/l953 Glasgow et al 122/RU en, N. Dak. 2,684,662 7 1954 Hull 122/140 [2]] Appl. No. 847,656 2,729,200 l/l956 Miller l22/l40 :gzg Pn'mary ExaminerKenneth W.Sprague [73] Assignee Mr Hum-s, Inc Attorneys-Clarence A. 0 Bnen and Harvey B. Jacobson [54] STEAM GENERATING SYSTEM 6Dra Figs. Clams wing ABSTRACT: A steam generating system comprising an en- 1 larged water tank receiving an elongated fire tube "2/405 therethrough. The fire tube has a burner and steam coil l mounted on a movable frame [herein and electively retractaof ble therefrom into an enclosed control room provided at one 406 end of the water tank and including controls, pump means,

cleaning means, and the like. The tire tube acts so as to pre- 1181mm Cm heat the water subsequently pumped from the tank and UNITED STATES PATENTS through the steam generating coil for ultimate discharge from 2,420,23l 5/1947 Crotty l22/RU the system.

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SHEET 2 BF 3 E rnesf R. Muclre/rath IN ll/V701: avian STEAM GENERATING SYSTEM The instant invention is generally concerned with steam generating systems, and more particularly relates to an all weather compact mobile system specifically adapted for outdoor use.

It is a primary object of the instant invention to provide a self-contained steam generating system that is particularly adapted to operate under extremely cold weather conditions, utilizing any available water supply.

Another significant object of the instant invention resides in the provision of a mobile system, either skid or wheel mounted.

In addition, it is considered significant that the system of the instant invention incorporate, on the mobile base, an enclosed control room which can be independently heated so as to prevent the freezing and maintain the operability of the various controls.

Also of significance in the instant invention is the orientation of the steam generating coil on a mobile frame within an elongated fire tube, for selective removal therefrom, the fire tube itself extending through the interior of the water tank from which the water to be generated into steam is drawn. In this manner, a preheating of the water within the tank will be efiected, thus enabling a reduction in the effective length of the coil and other resultant economies in both time and materials.

As another feature, the instant invention also contemplates the provision of means whereby the generated steam can be recirculated through the water containing tank so as to enable a rapid preheating thereof, such being effected, as one example, as the mobile unit is being transported to the work site.

Basically, the objects of the instant invention are provided for through the utilization of an elongated base mounted water tank having a control room at one end thereof, the tank itself containing an elongated fire tube into which a steam coil and burner unit can be introduced for operation both so as to generate steam and preheat the surrounding water, the products of combustion being discharged through the flue end of the fire tube. Flow lines are provided so as to move the water under pressure from the water tank through the steam coil and out to the work site. Alternatively, the generated steam can be introduced into the tank so as to form a closed recirculating system, thereby effecting a rapid preheating of the water in the tank, the tank water also of course being preheated by the tank received fire tube itself.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

FIG. 1 is a perspective view of the steam generating apparatus of the instant invention;

FIG. 2 is an enlarged cross-sectional view taken substantially on a plane passing along line 2-2 in FIG. 1;

FIG. 3 is a transverse cross-sectional view taken substantially on a plane passing along line 3-3 in FIG. 2;

FIG. 4 is a transverse cross-sectional view taken substantially on a plane passing along line 4-4 in FIG. 2;

FIG. 5 is a partial longitudinal cross-sectional view through the water tank and control room with the frame mounted coil and burner unit removed; and

FIG. 6 is a perspective view of the frame mounted coil and burner unit.

Referring now more specifically to the drawings, reference numeral 10 is used to designate the steam generating apparatus of the instant invention. The apparatus 10 includes an enlarged horizontally orientated cylindrical housing 12, externally insulated and internally divided into an enlarged water tank or chamber 14 and a relatively smaller control room 16 by means of a transverse bulkhead 18. The housing 12 is mounted on a mobile platform or base 20 incorporating, in the illustrated embodiment, a pair of ground skids 22. It should also of course be appreciated that, for the purpose of increasing the mobility of the unit 10, wheels can be substituted for, or in fact mounted on, the skids 22.

A right angularly formed elongated hollow fire tube or fire chamber 24 is positioned within the water tank 14. This fire tube 24 includes a horizontal leg or section 26 extending along the length of the water tank 14 through and slightly beyond the bulkhead 18 to which it is peripherally sealed, as by welding or the like. The second section 28 of the fire tube 24 communicates directly with and projects vertically from the inner end of the horizontal section 26 and extends through and above the housing 12, as well as the insulating covering thereon. This vertical section 28 acts in the manner of a flue and pivotally mounts a stack head 30 on the upper end thereof which can be folded down, as suggested in phantom lines in FIG. 2, to a retracted position lying against the end wall of the water tank 14 whereby the height of the apparatus is reduced for road travel purposes. In its erected position, it will be appreciated that the cap 30 incorporated a peripheral flange 32 about the lower end thereof which seats on a similar flange 34 about the upper end of the fire tube section 28, with appropriate bolt or other means 36 engaged therebetween.

It willbe noted that the water tank 14 is substantially enlarged relative to the fire tube 24, with the horizontal section 26 of the fire tube 24 extending through substantially the entire length of the tank 14, and the vertical section 28 of the fire tube 24 extending through substantially the entire height of the tank 14 so as to obtain maximum heat exchanging contact with the water supply within the tank. In this manner, a highly efficient utilization of the fire tube as a means for preheating the water supply is effected. Incidentally, it will be appreciated that, in order to accommodate substantially full length and full height fire tube sections within the water tank 14, the horizontal section 26 is orientated toward the lower end of the tank, while the vertical section 28 is located toward the outer end wall of the tank, the fire tube 24 itself being of a constant cross-sectional area throughout the length thereof, enlarging slightly at the angular corner therebetween whereby a positive unencumbered flow of the heated'air therewithin is provided for.

Positioned longitudinally within the horizontal fire tube section 26 is an elongated steam coil 38, the convolutions of the steam coil 38 defining a hollow cylindrical core completely therethrough for the accommodation of the heated discharge of the heat source or burner 40 longitudinally aligned therewith rearwardly thereof, also within the horizontal section 26 of the fire tube 24. The outer end of the horizontal section 26, adjacent which the burner 40 is positioned, is closed by a hingedly mounted closure or door panel 42 which can be selectively swung open, as suggested in FIG. 5, so as to allow access to the fire tube 24. In addition, appropriate means can be provided in association with the panel 42 so as to maintain the panel in a tube closing position. Immediately forward of the closure panel 42, the lower portion of the horizontal section 26 is provided with an enlarged downwardly directed opening 44 which acts as a combined air inlet for the burner 40 and access port for the various lines associated with the burner and steam coil. Such lines include a fuel line 46 releasably coupled with the burner 40 and extending therefrom to an enlarged fuel tank 48 mounted on the mobile base 20 beyond the outer end wall of the water tank 14. The actual fuel utilized can be of any appropriate type, such as gas or oil. Also extending through the access port 44 are a coil connected flexible water line 50 and a coil connected flexible steam line 52 engaged with the appropriate opposite ends of the coil 38. The water line 50 is communicated with a motor driven pump 54, which is in turn communicated with the interior of the tank 14 by a second water line 56 whereby water is removed from the tank 14 and introduced into the steam coil 38 under pressure. The steam line 52 extends through the sidewall of the control room 16 and mounts a control valve and nozzle unit 58 on the outer end thereof. A bypass steam line 60 is engaged, through an appropriate valve unit 62, with the steam line 52 just inward of the control room wall and extends therefrom into the interior of the water tank 14 whereby, through a manipulation of the valve unit 62, the steam can be selectively directed to the exterior discharge nozzle unit 58 or reintroduced into the water tank M. This arrangement is particularly significant in providing for a rapid preheating of the water supply, the recirculation system provided by the bypass steam line 60 being utilized, as one example, when moving the apparatus to the work site so as to enable an immediate use thereof upon arrival at the work site.

Both the steam coil 38 and the burner 40 are mounted, through depending leg means 64, on a pair of opposed runners 66 which are in turn slidably engaged within longitudinally extending guides 68 extending inwardly of the panel closed outer end of the horizontal section 26, thus providing a movable frame for the coil and burner. By mounting the coil and burner on a movable frame, it will be appreciated that the coil and burner can be retracted as a unit from the fire tube 24 for servicing or the like either with or without uncoupling the flexible water and steam lines, the outward swinging of the closure panel 42 allowing for a movement of the support frame into the control room 16. Incidentally, it should of course be appreciated that various other types of mobile frames can be utilized, however, such frames should present a minimum amount of obstruction within the interior of the fire tube 241 while at the same time providing for a firm stable support of both the coil 38 and the burner 40. Furthermore, it will be appreciated that the coil 38 extends only approximately to the inner side of the lower end of the vertical fire tube section 28, thereby not interfering with the free passage of the heated air from the horizontal section 26 to the vertical section 28.

Inasmuch as the apparatus of the instant invention is particularly adapted for field use, in most instances in remote locations, it is essential that it be adapted to accommodate water from any available source, whether treated or untreated. Accordingly, the apparatus incorporates its own cleaning system for the pump and coil. This system consists of an enlarged chemical tank 70 mounted with the control room 16 and adapted to have the water line 56 selectively connected to a valve controlled discharge 72 thereon for a passage of the chemical cleaning agent through the pump and coil. By the same token, if so desired, the steam discharge line 52 can also be communicated with the chemical tank 70 so as to provide a recirculating system for the cleaning chemical, Where appropriate, such as whendisengaging the water line 56 from the tank 14 for engagement with the chemical tank 70, suitable cutoffs can be provided. Furthergauxiliary valve control flow lines can, if deemed desirable, be permanently hooked up between the chemical tank 70 and the pump 5 the primary consideration being the provision of means for effecting a selective circulation of an appropriate cleaning chemical through the pump and coil. Incidentally, it should also be noted that the interior of the tank M can be selectively drained and cleaned through an appropriate drainage port 7d, a removable closure plate 76 being provided therefor.

it is contemplated that the apparatus of the instant invention be operative under extreme cold conditions. Accordingly, the control room 16 is provided with an internal heater 78, independently powered and specifically provided so as to keep the various controls within the control room 16 from freezing, particularly prior to an activation of the steam generating apparatus. In addition to this, as mentioned previously, the entire exterior of the tank and control room housing 12 is provided with an insulated covering, the door 80 through the outer end wall of the control room 16, which provides access thereinto, is also of course insulated and includes an appropriate air vent. As will be appreciated, the control room 16 will contain all the necessary controls and gauges required for the operation of the apparatus, several of which, including a tank water temperature gauge 82, and a steam gauge 84, have been illustrated.

From the foregoing, it will be recognized that a highly unique steam generating system has been defined. The ap paratus which constitutes the system is self-contained,

mounted on a unitary base, and incorporates a single elon-' gated housing within which both a water tank and a closed control room are defined. The actual steam generating apparatus is orientated within a fire tube extending through the water tank and connected thereto by appropriate water line means. The steam coil and associated burner are mounted on a mobile frame which can be selectively withdrawn from the fire tube and into the control room for cleaning and the like. In addition, means are incorporated directly in the apparatus for the circulation of cleaning chemicals through the coil whereby a periodic cleaning thereof is easily effected, this in turn allowing for the use of water from any available source without requiring a pretreating thereof.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

What I claim as new is as follows:

1. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil within a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, steam discharge line means extending from said steam coil, a control room mounted adjacent said water tank, the first end portion of said fire tube extending into said control room, and closure means mounted on said fire tube and selectively closing the first end thereof, the means mounting said heat source and steam coil comprising a frame movably mounted within the fire tube and selectively projectable beyond the first end thereof for at least a partial withdrawal of the heat source and steam coil from the fire tube.

2. The system of claim ll wherein said fire tube comprises a horizontal section extending inwardly from the first end thereof, and a vertical section extending vertically upward from the horizontal section at the end thereof remote from the first end of the fire tube, said vertical section terminating at the second end of the fire tube outward of the water tank.

3. The system of claim 2 including means for selectively communicating the steam discharge line means with the water supply to provide a circulating system and an accelerated preheating of the water supply.

4. The system of claim 3 including a mobile base supporting said water tank and said control room.

5. The system of claim 4 wherein the water tank and control room are formed in a continuous cylindrical housing with opposed end walls and an internal bulkhead dividing the housing into the tank and control room.

6. The system of claim 5 including a fuel supply tank mounted on said mobile base, and fuel supply line means communicating the fuel supply tank with the heat source.

7. The system of claim 6 including a chemical supply tank mounted within the control room, and means associated with the chemical supply tank for a selective flushing of the steam coil with the contents thereof.

8. The system of claim 7 wherein the second end of the fire tube projects a substantial distance above the water tank and terminates in a flue cap, said fiue cap being pivotally mounted on the fire tube and selectively collapsible downwardly so as to reduce the overall height of the apparatus.

Q. The system of claim 8 wherein the water tank and control room are exteriorly insulated.

10. The system of claim 9 wherein said steam coil is positioned solely within the horizontal fire tube section, said fire tube being of a substantially constant cross section throughout the full length thereof.

11. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil within a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, and steam discharge line means extending from said steam coil, the means mounting said heat source and steam coil comprising a frame movably mounted within the fire tube and selectively projectable beyond the first end thereof for at least a partial withdrawal of the heat source and steam coil from the fire tube.

12. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil with a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, and steam discharge line means extending from said steam coil, said fire tube comprising a horizontal section extending inwardly from the first end thereof, and a vertical section extending vertically upward from the horizontal section at the end thereof remote from the first end of the fire tube, said vertical section terminating at the second end of the fire tube outward of the water tank.

13. The system of claim 12 wherein said steam coil is positioned solely within the horizontal fire tube section, said fire tube being of a substantially constant cross section throughout the full length thereof.

14. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil within a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, steam discharge line means extending from said steam coil, and means for selectively communicating the steam discharge line means with the water supply to provide a circulating system and an accelerated preheating of the water supply.

15. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil within a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, and steam discharge line means extending from said steam coil, the water tank and control room being formed in a continuous cylindrical housing with opposed end walls and an internal bulkhead dividing the housing into the tank and control room.

16. The system of claim 15 including a chemical supply tank mounted within the control room, and means associated with the chemical supply tank for a selective flushing of the steam coil with the contents thereof.

17. The system of claim 15 including independently operable heating means within said control room for independently maintaining an elevated temperature therein sufi'icient so as to maintain the controls therein operable.

18. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam generating heat exchange unit, means mounting said heat source and said steam generating heat exchange unit within a first end portion of said fire tube, said heat exchange unit being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end of said fire tube constituting a discharge flue, water line means communicating the water supply with the heat exchange unit, and steam discharge line means extending from said heat exchange unit, the means mounting said heat source and said steam generating heat exchange unit comprising a frame movably mounted within the fire tube and selectively projectable beyond the first end thereof for at least a partial withdrawal of the heat source and heat exchange unit from the fire tube.

19. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam generating heat exchange unit, means mounting said heat source and said steam generating heat exchange unit within a first end portion of said fire tube, said heat exchange unit being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end of said fire tube constituting a discharge flue, water line means communicating the water supply with the heat exchange unit, steam discharge line means extending from said heat exchange unit, and means for selectively communicating the steam discharge line means with'the water supply to provide a circulating system and an accelerated preheating of the water supply. 

1. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil within a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, steam discharge line means extending from said steam coil, a control room mounted adjacent said water tank, the first end portion of said fire tube extending into said control room, and closure means mounted on said fire tube and selectively closing the first end thereof, the means mounting said heat source and steam coil comprising a frame Movably mounted within the fire tube and selectively projectable beyond the first end thereof for at least a partial withdrawal of the heat source and steam coil from the fire tube.
 2. The system of claim 1 wherein said fire tube comprises a horizontal section extending inwardly from the first end thereof, and a vertical section extending vertically upward from the horizontal section at the end thereof remote from the first end of the fire tube, said vertical section terminating at the second end of the fire tube outward of the water tank.
 3. The system of claim 2 including means for selectively communicating the steam discharge line means with the water supply to provide a circulating system and an accelerated preheating of the water supply.
 4. The system of claim 3 including a mobile base supporting said water tank and said control room.
 5. The system of claim 4 wherein the water tank and control room are formed in a continuous cylindrical housing with opposed end walls and an internal bulkhead dividing the housing into the tank and control room.
 6. The system of claim 5 including a fuel supply tank mounted on said mobile base, and fuel supply line means communicating the fuel supply tank with the heat source.
 7. The system of claim 6 including a chemical supply tank mounted within the control room, and means associated with the chemical supply tank for a selective flushing of the steam coil with the contents thereof.
 8. The system of claim 7 wherein the second end of the fire tube projects a substantial distance above the water tank and terminates in a flue cap, said flue cap being pivotally mounted on the fire tube and selectively collapsible downwardly so as to reduce the overall height of the apparatus.
 9. The system of claim 8 wherein the water tank and control room are exteriorly insulated.
 10. The system of claim 9 wherein said steam coil is positioned solely within the horizontal fire tube section, said fire tube being of a substantially constant cross section throughout the full length thereof.
 11. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil within a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, and steam discharge line means extending from said steam coil, the means mounting said heat source and steam coil comprising a frame movably mounted within the fire tube and selectively projectable beyond the first end thereof for at least a partial withdrawal of the heat source and steam coil from the fire tube.
 12. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil with a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, and steam discharge line means extending from said steam coil, said fire tube comprising a horizontal section extending inwardly from the first end thereof, and a vertical section extending vertically upward from the horizontal section at the end thereof remote from the first end of the fire tube, said vertical section tErminating at the second end of the fire tube outward of the water tank.
 13. The system of claim 12 wherein said steam coil is positioned solely within the horizontal fire tube section, said fire tube being of a substantially constant cross section throughout the full length thereof.
 14. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil within a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, steam discharge line means extending from said steam coil, and means for selectively communicating the steam discharge line means with the water supply to provide a circulating system and an accelerated preheating of the water supply.
 15. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam coil, means mounting said heat source and steam coil within a first end portion of said fire tube, said coil being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end portion of said fire tube constituting a discharge flue, water line means communicating the water supply with the steam coil, and steam discharge line means extending from said steam coil, the water tank and control room being formed in a continuous cylindrical housing with opposed end walls and an internal bulkhead dividing the housing into the tank and control room.
 16. The system of claim 15 including a chemical supply tank mounted within the control room, and means associated with the chemical supply tank for a selective flushing of the steam coil with the contents thereof.
 17. The system of claim 15 including independently operable heating means within said control room for independently maintaining an elevated temperature therein sufficient so as to maintain the controls therein operable.
 18. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam generating heat exchange unit, means mounting said heat source and said steam generating heat exchange unit within a first end portion of said fire tube, said heat exchange unit being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end of said fire tube constituting a discharge flue, water line means communicating the water supply with the heat exchange unit, and steam discharge line means extending from said heat exchange unit, the means mounting said heat source and said steam generating heat exchange unit comprising a frame movably mounted within the fire tube and selectively projectable beyond the first end thereof for at least a partial withdrawal of the heat source and heat exchange unit from the fire tube.
 19. A steam generating system comprising a water supply containing water tank, an elongated fire tube extending through said tank for a preheating of the water therein, said fire tube having opposed ends communicating with the exterior of said tank at a pair of spaced points, a heat source and an associated steam generating heat exchange unit, means mounting said heat source and said sTeam generating heat exchange unit within a first end portion of said fire tube, said heat exchange unit being orientated inward of said heat source along the flow path of the heat produced by the heat source, the second end of said fire tube constituting a discharge flue, water line means communicating the water supply with the heat exchange unit, steam discharge line means extending from said heat exchange unit, and means for selectively communicating the steam discharge line means with the water supply to provide a circulating system and an accelerated preheating of the water supply. 